Photographic process comprising improved dye bleaching step

ABSTRACT

AN IMPROVED PHOTOGRAPHIC PROCESS COMPRISING AN IMPROVED AND RAPID DYE BLEACHING STEP COMPRISES: (1) EXPOSING TO AN IMAGE PATTERN OF ACTIVATING RADIATION A DYESENSITIZED PHOTOSENSITIVE COPY MEDIUM WHICH BECOMES ACTIVATED AT PORTIONS THEREOF WHICH ARE EXPOSED TO SUCH ACTIVATING RADIATION AND, (2) APPLYING TO THE EXPOSED MEDIUM A DYE BLEACHING SOLUTION OF A SOLVENT SOLUBLE THIONATE SELECTED FROM AT LEAST ONE OF THE GROUP OF SULFITES AND BISULFITES AND ESPECIALLY THOSE OF GROUPS I-A AND II-A METALS, SAID THIONATE HAVING A CONCENTRATION OF AT LEAST ABOUT 0.1 MOLE OF THIONATE PER LITER OF SOULTION; AN AMIDE, SAID AMIDE HAVING A CONCENTRATION OF FROM ABOUT 0.5 TO 15.0 MOLES OF AMIDE PER LITER OF SOLUTION; AND OPTIONALLY AN ETHER, SAID ETHER HAVING A CONCENTRATION OF FROM ABOUT 0 TO 2.0 MOLES OF ETHER PER LITER OF SOLUTION. THIS DYE BLEACHING SOLUTION CAN BE APPLIED T THE PHOTOSENSITIVE COPY MEDIUM ALONG WITH THE IMAGEFORMING MATERIAL, STABILIZING BATH, FIXING BATH, STOP BATH, OR WASHING-AID BATH. IN A PREFERRED EMBODIMENT, THE DYE BLEACHING SOLUTION IS COMBINED WITH THE STABILIZING OR FIXING BATH. IN SUCH AN EMBODIMENT WHEREIN THE THIONATE IS POTASSIUM SULFITE AND THE STABILIZING OR FIXING BATH IS AN AQUEOUS SOLUTION OF SODIUM THIOSULFATE, THE POTASSIUM SULFITE SERVES THE DUAL FUNCTION OF A BLEACHING AGENT FOR A COLORED DYE-SENSITIVE COPY MEDIUM AND ALSO A PRESERVATIVE FOR THE SODIUM THIOSULFATE.

3,634,263 PHOTOGRAPHIC PROCESS COMPRISING INIPROVED DYE BLEACHIN G STEP Paul Andrew Jargiello, Lexington, Mass., assignor to Itek Corporation, Lexington, Mass.

No Drawing. Original application May 25, 1967, Ser. No. 641,127, now Patent No. 3,520,688, dated July 14, 1970. Divided and this application Sept. 22, 1969, Ser. No. 870,870

Int. Cl. Clld 7/54 U.S. Cl. 252-402 16 Claims ABSTRACT OF THE DISCLOSURE An improved photographic process comprising an in1- proved and rapid dye bleaching step comprises: (1) exosing to an image pattern of activating radiation a dyesensitized photosensitive copy medium which becomes activated at portions thereof which are exposed to such activating radiation and, (2) applying to the exposed medium a dye bleaching solution of a solvent soluble thionate selected from at least one of the group of sulfites and bisulfites and especially those of Groups I-A and ILA metals, said thionate having a concentration of at least about 0.1 mole of thionate per liter of solution; an amide, said amide having a concentration of from about 0.5 to 15.0 moles of amide per liter of solution; and optionally an ether, said ether having a concentration of from about to 2.0 moles of ether per liter of solution. This dye bleaching solution can be applied to the photosensitive copy medium along with the imageforming material, stabilizing bath, fixing bath, stop bath, or washing-aid bath. In a preferred embodiment, the dye bleaching solution is combined with the stabilizing or fixing bath. In such an embodiment wherein the thionate is potassium sulfite and the stabilizing or fixing bath is an aqueous solution of sodium thiosulfate, the potassium sulfite serves the dual function of a bleaching agent for a colored dye-sensitive copy medium and also a preservative for the sodium thiosulfate.

This application is a division of Ser. No. 641,127 filed May 25, 1967, now U.S. Pat. No. 3,520,688.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to the field of photographic reproduction systems, and, more specifically, to a photographic system utilizing an improved copy medium comprising a photosensitive material sensitized with a bleach able dye, which photosensitive material when activated by suitable means, is capable of producing a visible image.

(2) Description of the prior art Data or image storage media comprising radiationsensitive materials such as titanium dioxide are described in detail in U.S. Pats. 3,152,903; 3,152,904; 3,052,541; French Pats. 345,206 and 1,245,215 and in commonlyowned co-pending U.S. application Ser. No. 199,211, filed May 14, 1962 in the names of Elliot Berman et al., now abandoned. In the aforementioned U.S. patent application, radiation-sensitive titanium dioxide functions as a photosensitive component of the media and exposure of said media to activating means such as radiant energy, electron beams or the like results in the storage of a reversible latent image pattern therein. The reversible latent image pattern exists for a limited time during which said pattern can be converted to an irreversible form and read out visually by contacting said pattern with a suitable image forming material, such as a chemical redox system.

ed States Patent 0 3,634,263 Patented Jan. 11, 1972 In the aforesaid U.S. and French patents, the radiationsensitive material is combined with at least one component of an image-forming material prior to exposure to activating means. For example, U.S. Pat. 3,152,904 describes a photosensitive copy media comprising a photosensitive material such as titanium dioxide in combination with a reducible metal ion such as silver nitrate. This copy media is exposed to activating means to produce a visible image. On the other hand, U.S. Pat. 3,152,903 discloses a system wherein the photosensitive material is used in combination with both an oxidizing agent such as silver nitrate and a reducing agent such as hydroquinone. Upon exposure to suitable activating means, a visible image is formed.

One of the features of the above-mentioned data or image storage systems is that the photosensitive materials are often sensitive to a very narrow range of electromagnetic radiation. Therefore, it is often desirable to sensitize these photosensitive materials to additional ranges of electromagnetic radiation by application of dyes. Such dyes are well known to the art and include, for example, cyanine dyes, dicarbocyanine dyes, the carbocyanine dyes, and the hemicyanine dyes. Such dye-sensitized systems are disclosed in co-pending application U.S. Ser. No. 432,887 filed Feb. 15, 1965, in the names of E. Berman et al., copending application U.S. Ser. No. 359,956 filed Apr. 15, 1964 in the names of R. F. Bartlett et al., now U.S. 3,414,- 410, and co-pending application U.S. Ser. No. 633,689 filed Apr. 26, 1967 in the names of J. H. H. Keller and R. S. Sprague.

One of the problems with using such dyes to sensitize the photosensitive medium is the removal of the dye after development of the latent image to a visible image in order to obtain a final print with a white background. In the past this dye removal has been accomplished by dissolving the dye out of the substrate or by contacting with a suitable oxidizing agent. However, these methods have either been extremely slow or the oxidizing agent has been so strong that it produced detrimental effects upon the visible image formed in the final print. Co-pending application U.S. Ser. No. 641,216 filed May 25, 1967 in the names of R. C. Beach et al. entitled Photographic Process Comprising Dye Bleaching Step, teaches that a dye which has been incorporated in a photosensitive medium can be bleached by a solution of a solventsoluble thionate selected from at least one of the group of sulfites and bisulfites wherein the concentration of the thionate is at least about 0.5 moles per liter of solution. However, one of the serious limitations of this process and dye bleaching solution is that the dye is generally incompletely bleached or if complete bleaching is achieved, it is only after a very prolonged period of time.

SUMMARY OF THE INVENTION It has now been unexpectedly found that a photosensitive medium sensitized with a bleachable dye in the colored form may be rapidly converted to the colorless state without detrimental effects to the final print when contacted with an improved dye-bleaching solution of (1) a solvent-soluble thionate selected from at least one of the group of the sulfites and bisulfites and especially those thionates of the metals of Groups I-A and II-A of the Periodic Table, prefer-ably having a concentration of from about 0.1 moles of thionate per liter of solution to a solution being saturated with the thionate, (2) an amide in which the dye being bleached is soluble, said amide having a concentration of from 0.5 to 15.0 moles of amide per liter of solution, and optionally (3) an ether in which the dye being bleached is at least partially 1 Periodic Table from Langes Handbook of Chemistry, 9th edition, pp, 56-57.

oluble, said ether having a concentration of from O to 2.0 holes of ether per liter of solution. More particularly, his invention involved a process for recording an image Iattern of activating radiation comprising exposing to n image pattern of activating radiation a photosensitive opy medium sensitized with a bleachable colored dye which becomes activated at portions thereof which are xposed to activating radiation, wherein the improvement omprises applying to the exposed copy medium an imroved dye bleaching solution as above described. In a Ireferred process, the thionate is incorporated in imageorming material, in stabilizing bath, in fixing bath, or r1 stop bath which is applied to an exposed and developed hotosensitive copy medium. Therefore, a preferred em- =odiment comprises a photosensitive copy medium sensiized with a bleachable dye which is exposed to an image attern of activating radiation, then contacted with an xidizing agent such as a solution of silver nitrate, then ontacted with a solution of a reducing agent such as Jetol, and finally contacted with a combined stabilizing ath and dye-bleaching solution comprising, for example, odium or ammonium thiosulfate, potassium sulfite, an mide and an ether, either of which amide and ether are apable of dissolving, at least partially, the dye which being bleached.

A preferred process comprises a heating step subseuent to the step of contacting the dye-sensitized copy aedium with the dye-bleaching composition of this inention. Heat acts to further accelerate the dye-bleaching -rocess.

DESCRIPTION OF PREFERRED EMBODIMENT(S) The thionates of the improved dye-bleaching solution of his invention are preferably selected from at least one of he solvent-soluble sulfites and bisulfites and more esecially those of Groups I-A and IIA metals. Potassium ulfite and bisulfite are especially preferred because of heir increased solubility in an aqueous solution. Any solent which does not significantly interfere with the rection may be used in the improved dye-bleaching comosition of this invention. Polar solvents are generally referred. Water is especially preferred as a solvent beause of its economy.

The thionates of this invention may be incorporated n any of the image-forming materials or in the stabilizng bath. The stabilizing bath used to fix or stabilize the eveloped print are those fixing or stabilizing baths such s described in the silver halide photographic arts, such s potassium thiocyanate solution, sodium thiosulfate olution, or solutions of other sulfur compounds. Suitably, he fixing or stabilizing baths contain a material which omplexes excess metal ion which may be present on the eveloped and amplified image areas as well as the non- ?nage areas, and prevents its further deposition as free rietal. When silver ion is present, for example, water oluble thiosulfates such as potassium thiosulfate or soium thiosulfate are usually used as complexing agents 1 the fixing bath.

The amides useful in the improved dye bleaching soluion of this invention are those in which the dye being leached is at least partially soluble. Suitable amides re those of the general formula Jherein R, R and R may be the same or difi'erent, nd may be any of hydrogen, alkyl, aryl, aralkyl, and lkaryl groups, wherein R or R may be an roup, and wherein R and R may form part of the ante ring structure, thus forming a substituted or unsub= stituted cycloalkylene or aryl structure. Preferred amides are those wherein R, R or R are hydrogen or groups containing 1-0 or less carbon atoms. Exemplary of the amides which are useful in this invention are the following: formamide, acetamide, dimethyl formamide, dimethyl acetamide, benzamide, stearamide, and the higher amides such as diacetamide, (CH CO) NH, and triacetamide, (CI-I CO) N.

Suitable ethers which can optionally be added to the improved dye-bleaching solutions of this invention are those of the formula R OR wherein R and R may be the same or different and represent hydrocarbon groups such as alkyl, alkaryl, aryl and aralkyl groups. These hydrocarbon groups may be aliphatic, unsaturated, or aromatic, and their hydrogens may be replaced by other groups such as halogens or hydroxyl groups, e.g. 1- methoxy-2,3-propanediol. The ether group may also be present in ring compounds, such as dioxane. R and R4, may also represent ether groups themselves as for example in bis(2-methoxyethyl) ether. Examples of some suitable ethers, useful in this invention, are diethyl ether, methyl ether, bis(2-chloroethyl) ether, isopropyl ether, Cellosolve, diphenyl ether, bis(2-chloroisopropyl) ether, n-butyl ether, amyl ether, n-hexyl ether, bis(2-methoxyethyl) ether, and benzyl ether.

The protoconductor or photocatalyst preferred in this invention are metal containing photoconductors. A preferred group of such photosensitive materials are the inorganic materials such as compounds of a metal and a non-metallic element of Group VI-A of the periodic table such as oxides, such as zinc oxide, titanium dioxide, zirconium dioxide, germanium dioxide, indium trioxide; metal sulfides such as cadmium sulfide (CdS), zinc sulfide (ZnS) and tin disulfide (SnS metal selenides such as cadmium selenide (CdSe). Metal oxides are especially preferred photoconductors of this group. Titanium dioxide is a preferred metal oxide because of its unexpectedly good results. Titanium dioxide having an average particle size less than about 250 millimicrons and which has been treated in an oxidizing atmosphere at a temperature between about 200 C. and 950 C. for from about 0.5 hour to about 30 hours is especially preferred, and more especially that titanium dioxide produced by high temperature pyrolysis of titanium halide.

Also useful in this invention as photoconductors are certain fluorescent materials. Such materials include, for example, compounds such as silver activated zinc sulfide, zinc activated zinc oxide, manganese activated zinc phosphate Zn (PO an admixture of copper sulfide, antimony sulfide (SbS) and magnesium oxide (MgO), and cadmium borate.

While the exact mechanism "by which the photoconductors of this invention work is not known, it is believed that exposure of photoconductors or photocatalysts of this invention to activating means causes an electron or electrons to be transferred from the valence band of the photoconductor or photocatalyst to the conductance band of the same or at least to some similar excited state whereby the electron is loosely held, thereby changing the photoconductor from an inactive form to an active form. If the active form of the photoconductor or photocatalyst is in the presence of an electron accepting compound a transfer of electrons will take place between the photographic and the electron accepting compound, thereby reducing the electron accepting compound. Therefore a simple test which may be used to determine whether or not materials have a photoconductor or photocatalytic effect is to mix the material in question with an aqueous solution of silver nitrate. Little, if any, reaction should take place in the absence of light. The mixture is then sub jected to light. At the same time that a control sample of an aqueous solution of silver nitrate alone is subjected to light, such as ultraviolet light. If the mixture darkens faster than the silver nitrate alone, that material is a photoconductor photocatalyst,

It is evident that the gap between the valence and the conducting band of a compound determines the energy needed to make electron transitions. The more energy needed, the higher the frequency to which the photoconductor will respond. It is known to the art that it is possible to reduce the band-gap for these compounds by adding a foreign compound as an activator which either by virtue of its atomic dimensions or by possessing a particular electronic forbidden zone structure or through the presence of traps as donor levels in the intermediate zone between the valence and the conduction band stresses the electronic configuration of the photoconductive compound, thereby reducing its band-gap and thus increasing its ability to release electrons to its conduction band. Phosphors almost necessarily imply the presence of such activating substances. The eifect of such impurities may be such as to confer photoconductivity upon a compound which intrinsically is nonphotoconductive. The (CrSr)S phosphors are believed to be an example of this group. On the other hand, excessive impurity content can interfere with a compound acting as a photoconductor, as above described.

Bleachable dyes useful for sensitizing the photosensitive copy medium of this invention include, for example, the cyanine dyes, the dicarbocyanine dyes, the carbocyanine dyes, and the hemicyanine dyes. Suitable cyanine dyes are the following:

3,3-diethyl-4,5,4,S'-dibenzothiacyanine chloride;

3-,B-carboxyethyl-1'-ethyl-6'-methoxy-S-phenyl-thia-Z'- cyanine iodide;

3,3-diethyl-4.5,4,5'-dibenzoxacyanine iodide;

3 ,3 '-diethylthiazolinocarbocyanine iodide;

3,3-diethyloxacarbocyanine iodide; and

3,3'-diethyl-9-methyloxaselenacarbocyanine iodide.

Suitable dicarbocyanine dyes are the following:

3,3-di-;8-hydroxyethylthiadicarbocyanine bromide;

anhydro-3 ,3 '-di-B-carboxyethylthiadicarbocyanine hydroxide;

3,3-diethyloxathiadicarbocyanine iodide;

3,3'-diethyl-4,5,4,5'-dibenzothiadicarbocyanine iodide;

3'-carboxymethyl-3-ethyloxathiadicarbocyanine iodide;

3-carboxymethyl-3-ethyloxathiadicarbocyanine iodide;

and

3,3'-di(carboxymethyl)oxathiadicarbocyanine bromide.

Suitable carbocyam'ne dyes are the following:

3,3'-diethyl-9-methyl-4,5,4',5',-dibenzothiacarbocyanine chloride; anhydro-3,3-di-,8-carboxyethyl-5,S'-dichloro-9-ethylthiacarbocyanine hydroxide; anhydro-3- 3-carboxyethyl-5,5-dichloro-9-ethyl-3'- B-sulfoethylthiacarbocyanine hydroxide; 9-ethyl-3,3-di-fl-hydroxyethylthiacarbocyanine iodide.

Suitable hemicyanine dyes are the following:

2-p-dimethylaminostyryl-4-methylthiazole methochloride; 2- [4- (p-dirnethylaminophenyl -l ,3-butadienyl]-1,3 ,3-

trimethylpseudoindolium chloride; 2- (p-dimethylaminostyryl -'b enzimidazole methochloride; 2- (pdimethylaminostyryl) -6-ethoxy-quinoline metho chloride; 6-dimethylamino-2- (p-dimethylaminostyryl) -quinoline methochloride; Z-p-dimethylaminophenyl-6-methylbenzothiazole methochloride (Thioflavine T); 3,3-dimethyl-2 [6 (p-dimethylaminophenyl) 1,3,5 -hexatrienylJindolenine ethiodide; 2 (p-dimethylaminostyryl -3,S-dimethylthiadiazolium nitrate; 2-p-dimethylaminostyryl-4-methylthiazole-,8-hydroxyetho-chloride; and 2-p-dimethylaminostyryl-S-methyl-1,3 ,4-thiadiazole-B- hy droxy-etho-chloride.

Aminostyryl hemicyanine dyes are an especially preferred class of dyes because of the improved photographic exposure speed and improved image densities for a given speed achieved with photosensitive copy media so sensit-ized.

Additional dyes which are useful for sensitizing the photosensitive medium of this invention are the cyanine dyes described on pages 371-429 in The Theory of Photographic Process by 'C. E. Kenneth Mees published by McMillan Company in 1952. Other useful dyes include those known to the art as triphenylmethane dyes such as crystal violet and basic Puchsin, diphenylmethane dyes such as Auroamine O, and Xanthene dyes such as Rhodamine B.

The dyes useful in this invention may be used in solution to treat the photosensitive materials prior to their incorporation into a copy medium. These dyed photosensitive materials can then be deposited on a substrate, or incorporated into a substrate such as a fibrous web of paper. Alternatively, the dye can be combined with the photoconductive materials in the copy medium as per example, by dispersion of the dye in the binder for the photosensitive material. In addition, it is possible to dip dye the photosensitive substrate by merely immersing a substrate containing the photosensitive material into a solution of the particular dye.

Irradiation sources which are useful in this invention includes any activating electromagnetic radiation. Thus actinic light, X-rays, or gamma rays are effective in exiting the photocatalysts. Beams of electrons and other like particles may also be used in the place of the ordinary forms of electromagnetic radiation for forming an image according to this invention. These various activating means are designated by the term activating radiation.

The inert carrier sheet upon which the photoconductor and dyes of this invention are deposited comprises any suitable backing of suflicient strength and durability to satisfactorily serve as a reproduction carrier. The carrier sheet may be in any form such as, for example, sheets, ribbons, rolls, etc. This sheet may be made of any suit-able materials such as wood, rag content paper, pulp paper, plastics such as, for example, polyethylene terephthalate (Mylar) and cellulose-acetate, cloth, metallic foil and glass. The preferred form of the carrier sheet is a thin sheet which is flexible and durable.

It is also useful to use a binder agent to bind the bleachable dye useful in this invention and photosensitive materials to the carrier sheet. In general, these binders are translucent or transparent so as not to interfere with transmission of light therethrough. Preferred binder materials are hydrophilic or hydrophobic organic materials such as resins. Examples of suitable resins are butadiene-styrene copolymer, poly(alkyl acrylates) such as poly(rnethyl methacrylate) polyamides, polyvinyl acetate, polyvinyl alcohol and polyvinylpyrrolidone.

The photoconductor should be conditioned in the dark before exposure. Such conditioning is generally conducted from one to twenty-four hours. After conditioning, the photoconductor is not exposed to light prior to its exposure to activating radiation for recording an image pattern.

The period of exposure will depend upon the intensity of the light source, particular photoconductor, the type and amount of catalyst, if any, and like factors known to the art. In general, however, the exposure may vary from about 0.001 second to several minutes.

Image-forming materials which are useful in this invention are those such as described in US. Pat. 3,152,903 and in co-pending application Ser. No. 199,211. These image-forming materials include preferably an oxidizing agent and a reducing agent. Such image-forming materials are often referred to in the art as physical developers. The oxidizing agent is generally the image-forming component of the image-forming material. However, this is not necessarily true. Either organic or inorganic oxidizing agents may be employed as the oxidizing component if the image-forming material. Preferred oxidizing agents :omprise the reducible metal ions having at least the xidizing power of cupric ion and include such metal ions LS Ag Hg, Pb, Au Au, Pt+ Pt, Ni+ Sn b+ Cu, and Cu. Other suitable oxidizing agents iseful in this invention as components of an image-formng material are permanganate (MnO ion, various euco dye materials such as disclosed in co-pendmg aplicatin Ser. No. 623,534 filed Mar. 19, 1967 in the name )f L. Case, and the like. Organic oxidizing agents include etrazolium salts, such as tetrazolium blue and red, and liphenyl carbozone, and genarcyl red 6B (methine dye).

The reducing agent component of the image-forming naterials of this invention are inorganic compounds such 1.8 the oxelates, formates, and ethylenediaminetetraacetate :omplexes of metals having variable valence; and organic :ompounds such as dihydroxybenzenes, ammophenols, ind aminoanilines. Also, polyvinylpyrrolidone, hydrazine, LIld ascorbic acid may be used as reducing agents in this nvention. Suitable specific reducing compounds include iydroquinone or derivatives thereof, oand p-amino- )henol, pmethylaminophenol sulfate, p-hydroxyphenyl glycine, oand p-phenylenediamine, 1-phenyl-3-pyrazolilone, alkali and alkaline earth metal oxalates and 'ormates.

Additionally, the image-forming materials or physical levelopers may contain organic acids or alkali metal salts hereof, which can react with metal ions to form complex netal anions. Further, the developers may contain other :omplexing agents and the like to improve image formaion and other properties found to be desirable in this art.

The invention above described is exemplified as follows:

Example 1 A photosensitive copy medium comprising a paper suport coated with a finely-divided titanium dioxide dis- Jersed in a polyvinyl alcohol binder which has been dyeensitized with 2-p-dimethylaminostyryl-4-methyl thiazole netho chloride is exposed to an image pattern from a ungsten light source for 1-2 seconds duration, thereby giving an exposure of 400 meter candle seconds.

The thus-exposed copy medium is then immersed 0.28 ;econd in an aqueous solution of 0.32 molar silver nitrate, hen immersed 0.6 second in an aqueous developing soluion comprising Metol (p-methylaminophenol sulfate), hen immersed in a combined dye-bleaching and fixer- ;tabilizer bath of the following composition for 1 second:

Potassium sulfite (K SO )O grams Sodium thiosulfate (Na S O -SH O)-200 grams Glacial acetic acid-23 milliliters Dilute to 1 liter with water.

The copy medium is then allowed to sit for seven minutes 1nd then tested on a MacBeth densitometer read through 1 blue filter to determine the completeness of bleaching. ["he densitometer reading gives a relative measure of the :ompleteness of bleaching. The more complete the bleachng, the lower the optical density will be. After seven ninutes the above-tested copy medium was substantially :ompletely bleached, bein g converted from a bright orange .0 white in the non-image areas of the copy medium. The mage areas of the copy medium were not adversely afected by the bleaching process. Seven minutes after renoval of the copy medium from the bleach-fixer bath, he densitometer reading of the above-mentioned copy nedium was 0.15.

When 1.1 moles of acetamide is added to the above :olution and a copy medium is otherwise exposed and )rocessed in the manner above described gives an optical lensity on the MacBeth densitometer of 0.11 seven minutes ifter removal of the copy medium from the bleach-fixer )ath. Thus it can be seen that the addition of an amide o a sulfite bleaching solution increases markedly the conlersion of the colored dye to the colorless state. The color in the final print is decreased by 27% by the addition of the acetamide to the potassium sulfite bleach-fixer bath mentioned above.

Examples 2-10 A dye-sensitized TiO -coated copy medium of the composition described in Example 1 is exposed and treated as in Example 1 except that the combined dye-bleaching and fixing-stabilization bath is of the composition shown in Table I below. The optical density of the copy medium is measured seven (7) minutes after contacting the copy medium with the bleaching solution.

Acct-amide (moles) Dimethyl acetamide (moles) 1 2 Opticaldeusity .29 .22 .12 .17 .15 .17 .15

Weights are per liter of aqueous solution Examples 11-14 A dye-sensitized TiO -coated copy medium of the composition described in Example 1 is exposed and treated as per the procedure of Example 1, except that in place of the combined dye bleaching and fixing-stabilization bath a dye-bleaching solution is substituted having the compositions given in Table II below.

TABLE II Example No.

Acetamide (moles) 2.5 1.7 1. 2 1.7 Sodium thiosulfate (N 2128203) (grams) 50 Sodium sulfite (N 21 803) (grams) Potassium sulfite (KZSOS) (grams) 1 Weights are per liter of aqueous solution.

The orange background of the dye-sensitized copy medium is turned brown and no bleaching occurred after contacting this copy medium with the bleaching solution of Example 11. The bleaching solution of Example 12 had no effect on the orange color of a similar medium. The bleaching solution of Example 13 caused substantially complete bleaching of the orange dye in about five minutes after removal of the copy medium from the dye bleaching solution. The bleaching solution of Example 14 caused substantially complete bleaching almost immediately (within one (1) minute) after removal of the copy medium from the bleaching solution.

Examples 13 and 14 are modified by applying a fixing bath of potassium thiosulfate immediately prior to the application of the respective dye-bleaching solutions. The results of applying the dye-bleaching solutions to these thus-modified processes are substantially the same as those for Examples 13 and 14 as described above.

Example 15 A dye-sensitized TiO -coated copy medium is prepared by dispersing a finely-divided titanium dioxide pigment in a polyvinyl alcohol binder and coating this composition on a paper substrate. This copy medium is then dye-sensitized by a solution of 2-[4-(p-dimethylaminophenyl) 1,3 butadienyl] 1,3,3 trimethylpseudoindolium chloride. The thus dye-sensitized copy medium was a bright blue color. This copy medium was then immersed in a combined dye-bleaching and fixing-stabilization bath of the following composition:

Potassium sulfite-400 grams Sodium thiosulfate-ISO grams Formamide-300 milliliters Aminobenzoic acid-l grams Water was added to make 1 liter of solution. Within a few minutes after removing the copy medium from the bath, it has turned from a bright blue color to a substantially white and fully-bleached condition. A combined dye-bleaching and fixing-stabilization bath of the same composition as described above except that the formamide is not present gives incomplete bleaching when a dyesensitized substrate as described above is immersed in such a bath. Thus the presence of formamide not only accelerates the bleaching process but also makes possible a more complete bleaching.

Example 16 A dye-sensitized TiO -coated copy medium of the composition described in Example 1 is exposed and treated as per the procedure of Example 1 except that the combined dye-bleaching and fixing-stabilization bath is of the following composition:

Potassium sulfite-100 grams Sodium thiosulfate100 grams Formamide3.9 moles Bis(2-methoxy ethyl) ether1.0 mole l-methoxy-Z,3propanediol-1.2 moles Water is then added to make up 1 liter of solution. The optical density of the background areas of the thustreated copy medium is .11 at the end of seven (7) minutes after removing from the bleach-fixer solution.

Example 17 A dye-sensitized TiO -coated copy medium of the composition described in Example 1 is exposed and treated as per the procedure of Example 1 except that the combined dye-bleaching and fixing-stabilization bath is of the following composition:

Potassium sulfite-400 grams Sodium thiosulfate100 grams Formamide-5.5 moles Bis(2-methoxy ethyl) ether-.8 mole Water is then added to make up 1 liter of solution. The optical density of the background areas of the thustreated copy medium is .10 at the end of seven (7) minutes after removing from the bleach-fixer solution.

Example 18 A dye-sensitized TiO -coated medium of the composition described in Example 1 is exposed and treated as per the procedure of Example 1 except that the combined dye-bleaching and fixing-stabilization bath is of the following composition:

Potassium sulfite-400 grams Sodium thiosulfate-ISO grams Formamide.9.0 moles Water is added to make 1 liter of solution. Within about 75-90 seconds after removing the copy medium from this bleach-fixer bath, the orange-colored background areas of the copy medium appear to be completely bleached.

In the claims:

1. A composition for bleaching cyanine dyes, dicarbocyanine dyes, carbocyanine dyes or hemicyanine dyes consisting essentially of a solution of (l) a thionate selected from at least one member of the group consisting of the solvent-soluble sulfites and bisulfites in a concentration effective to bleach at least one of the above mentioned dyes, (2) an amide in which the dye to be bleached is at least partially soluble, said amide being present m a concentration sufficient to accelerate the dye bleaching, and optionally (3) an ether in which the dye to be bleached is at least partially soluble in a concentration .suflicient to accelerate the dye bleaching.

2. A dye-bleaching composition as in claim 1 wherein the thionate is a metal thionate of the Group I-A and Group II-A metals.

3. dye-bleaching composition as in claim 1 wherein the thionate is at least one of the group of sodium thionate and potassium thionate.

4. A dye-bleaching composition as in claim 2 wherein the solution is an aqueous solution.

5. A dye bleaching composition as in claim 1 wherein the amide is of the general formula wherein 'R, R and R may be the same or different, and may be any of hydrogen, alkyl, aryl, aralkyl, and alkaryl groups containing ten or less carbon atoms.

6. A dye-bleaching composition as in claim 1 wherein the amide is selected from the group of formamide, acetamide, dimethyl formamide and dimethyl acetamide.

7. A dye-bleaching composition as in claim 1 wherein the ether is bis(2-methoxy ethyl) ether.

8. A composition for bleaching cyanine dyes, dicarbocyanine dyes, carbocyanine dyes or hemicyanine dyes consisting essentially of a solution of (1) a thionate selected from at least one of the group of solvent-soluble sulfites and bisulfites of Group I-A and Group II-A metals, said thionate having a concentration of at least about 0.1 mole of thionate per liter of solution, (2) an amide in which the dye to be bleached is at least partially soluble, said amide having a concentration of from about 0.5 to 15.0 moles of amide per liter of solution, and optionally (3) an ether in which the dye to be bleached is at least partially soluble, said ether having a concentration of from about 0 to 2.0 moles of ether per liter of solution.

9. A dye-bleaching composition as in claim 8 wherein the thionate is potassium sulfite.

10. A dye-bleaching composition as in claim 8 wherein the amide is at least one of the group selected from formamide, acetamide, dimethyl formamide, and dimethyl acetamide.

11. A dye-bleaching composition as in claim 8 wherein the ether is bis(2-methoxy ethyl) ether.

12. A dye-bleaching composition as in claim 8 which is combined with a stabilizing bath.

13. A dye-bleaching composition as in claim 9 wherein the solution is an aqueous solution.

14. A dye-bleaching composition as in claim 12 wherein said stabilizing bath is a thiosulfate solution.

15. A composition for bleaching cyanine dyes, dicarbocyanine dyes, carbocyanine dyes or hemicyanine dyes consisting essentially of an aqueous solution of (1) potassium sulfite in a concentration eflective to bleach at least one of the above mentioned dyes, (2) an amide in which the dye to be bleached is at least partially soluble, said amide being present in a concentration sufficient to accelerate the dye bleaching, and (3) a thiosulfate compound in a concentration at least suflicient to act as a stabilizing bath for the photographic medium being developed.

16. A dye bleaching composition as in claim 15 wherein the concentration of potassium sulfite is about 200 grams per liter of solution, the thiosulfate compound is sodium thiosulfate in a concentration of about 200 grams per liter of solution, and the amide is acetamide in a concentration of about 1.1 moles per liter of solution.

References Cited UNITED STATES PATENTS 3,224,976 12./1965 Farrar et a1 252119 3,364,052 1/1968 Martino 252188 MAYER WEINBLATT, Primary Examiner US. Cl. X.R. 

